Hermetically sealed semiconductor power module and large scale module comprising the same

ABSTRACT

This is a semiconductor power module provided with: a ceramic substrate; a metallic plate bonded to a surface of this substrate; a cylindrical metallic flange which is hermetically bonded to a surface of substrate or the metallic plate; a ceramic housing for hermetically sealing an opening of the metallic flange; and at least one or more semiconductor chips soldered to the metallic plate. The metallic flange is made of metal with a low thermal expansion coefficient. A hermetically sealed container is created by welding the metallic flange, the ceramic substrate and the housing with silver brazing. Moreover, external collector, emitter and gate electrodes are bonded on the housing by using the silver brazing. The collector, emitter and gate conductive pillars are respectively connected to the external collector, emitter and gate electrodes with calking. Thus, this hermetically sealed container is strong in mechanical strength and high in explosion-proof durability and excellent in moisture resistance. And this semiconductor power module has a high TFT reliability and a high TCT reliability. Moreover, a power cycle durability is larger since the emitter pedals are pressure-contacted to the emitter electrode pads disposed on the semiconductor chip via the metallic hemispheres so as to implement a large conductive capacity.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor power modulewhich mounts a plurality of power semiconductor switches, such asinsulated gate bipolar transistors (IGBTs), gate turn-off (GTO)thyristors and the like in a single package, and a large scale modulecomprising a plurality of the semiconductor power modules. Moreparticularly, the present invention relates to the large scale modulesuitable for application fields in which various specifications arerequired as well as a high reliability for a long life. Especially, thepresent invention pertains to a power converter suitable for motioncontrol of an electric locomotive, in which very severe reliability fora long life is substantially supposed in nature.

[0003] 2. Description of the Related Art

[0004] As known in the art, the high frequency operation of the powerconverter can reduce the size and weight of the converter. And the powerconversion at higher and higher frequencies is desired for powerconverters used in control systems for driving electric locomotives,since the compactness and the light weight of the converters suitablefor installing in a railcar body are required to increase thetransportation efficiency. And the high frequency power conversion ofthe power converters can simultaneously satisfy the comfortableness ofpassengers in trains. However, the higher reliability, which willguarantee a long life, is also required for the railcar powerconverters. For example, the reliability, which will guarantee the longlife of more than about thirty years, is scheduled to be required forthe next generation railcar power converters

[0005]FIG. 1 is a broken sectional view showing an example of an innerstructure of a conventional plastic IGBT module used in such a powerconverter. A plastic side wall 2 is bonded to an edge of a metalliccooling plate 1. A plastic terminal cap 3 covers a top surface of thisplastic side wall 2. A copper plate 5, which is directly bonded orsilver-brazed to a bottom surface of a ceramic substrate 4, is solderedonto the metallic cooling plate 1 through a solder 6. A copper plateconstituting an emitter wiring pattern 71, a collector wiring pattern 72and a gate wiring pattern 73 is bonded on a top surface of the ceramicsubstrate 4. A semiconductor chip 8, such as IGBT chip and the like, issoldered to this copper plate 72 through a solder 13.

[0006] An emitter electrode pad on the surface of the semiconductor chip8 is electrically connected to the emitter wiring pattern 71 by aluminumbonding wires 91, and a gate electrode pad is electrically connected tothe gate wiring pattern 73 by an aluminum bonding wire 92. In addition,an emitter terminal 10, a collector terminal 11 and a gate terminal 12which are made of copper are respectively soldered through solders 13 tothe emitter wiring pattern 71, the collector wiring pattern 72 and thegate wiring pattern and are erected upwards. Heads of the emitterterminal 10, the collector terminal 11 and the gate terminal 12 areprotruding from the outer surface of the terminal cap 3, which supportsand fixes the emitter terminal 10, the collector terminal 11 and thegate terminal 12. Moreover, in order to shield the semiconductor chip 8from outside air, it is filled with a silicon resin 14, and an epoxyresin 15 is filled onto this silicon resin 14.

[0007] The semiconductor power modules used to control the system ofdriving the electric locomotive are required the high reliability underthe severe conditions of higher temperatures and higher humidities. Theabove mentioned conventional plastic IGBT module has the structuresealed with the silicon resin 14 or the epoxy resin 15. However, sincethis resin seal is of semi-seal structure, the conventional plastic IGBTmodule is of an incomplete sealed structure. Thus, the conventionalplastic IGBT module is weak in moisture resistance. So, under theenvironment of the high temperature and the high humidity, waterpermeates into the module to thereby cause the performance deteriorationof the semiconductor chip 8. This is undesirable in view of thereliability of a long time as the semiconductor power module for theelectric locomotive. In addition, there may be a possibility thatimpurities (sodium (Na), chromium (Cr) and the like) will gradually bedoped in the silicon resin used for the resin sealing. This impuritieswill invade the semiconductor chip 8 during the long operation. Thisresults in a problem that the reliability may be dropped.

[0008] Moreover, outer members 2, 3 constituting the semiconductor powermodule are made of plastic. Thus, they are also weak in mechanicalstrength. This results in a problem that the explosion-proof durabilityis substantially null when the semiconductor chip 8 is exploded by ashort circuit accident and the like.

[0009] Especially, some kinds of the electric locomotives, such as asuburban train, a subway transit car, a streetcar or the like,frequently repeat starts and stops. Thus, the semiconductor power moduleused therein are expected to have a very high power cycle durability.For example, a semiconductor power module for an railcar in a nextgeneration is planned to have a high power cycle durability of about tenmillion times, in a junction temperature variation ΔT_(j)=40° C. and ata case temperature T_(c)=50° C. However, in the above mentionedconventional plastic IGBT module, the semiconductor chip 8 and thewiring patterns 71, 72 and 73 made of the copper plates are connected toeach other through the aluminum bonding wires 91, 92. Hence, the powercycle durability of the conventional semiconductor power module is, forexample, only about one hundred thousand times at present. Therefore, itis difficult to satisfy the required power cycle durability for the nextgeneration railcar.

[0010] Moreover, the difference of the thermal expansion coefficientsbetween the metallic cooling plate 1 and the ceramic 4 is large, and therailcar frequently repeats the starts and the stops so as to causesevere temperature fluctuations. Then, the crack caused by the thermalstress due to the severe temperature fluctuations is induced in thesolder 6. This results in a problem that a Thermal Fatigue Test (TFT)reliability and a Thermal Cycling Test (TCT) reliability of theconventional semiconductor power module are both low and insufficient.On the contrary, the semiconductor power module for the electric railcarin the next generation is planed to have a TFT reliability of about 50thousands cycles at ΔT_(c)=70° C. (T_(c)=25° C. to 95° C.) and a TCTreliability of about 1000 cycles at ΔT_(c)=165° C. (T_(c)=−40° C. to125° C.). However, a present semiconductor power module attains a lowTFT reliability of about 5 thousands cycles and a low TCT reliability ofabout 100 to 300 cycles at the most, under the above mentionedconditions. This causes a problem that the planned specification willnot be attained in the next generation.

[0011] On the other hand, various power converters, such as a DC-DCconverter, a self-excitation inverter, a separate-excitation inverterand the like, are used in the respective control systems for driving themiscellaneous railcars. A rated specifications are variously changeddepending on the type of railcar systems. For example, the suburbantrain requires a large scale module, which comprises a plurality of thesemiconductor power modules, having a rated specification of a 800A,3300 V class or a 1200A, 3300V class. The Japanese high speed train(referred as “the Shinkansen” train in Japanese) requires the largescale modules having a rated specification of a 1200A, 4500V class. “TheInterCityExpress (ICE)”, the high speed train in Germany and Switzerlandor “the Train a Grande Vitesse (TGV)”, the high speed train in Francerequires the large scale modules having rated specification of 1200A,6500V classes. Then, various large scale modules having diversifiedrated specifications are required. Also, changes of the specification ofthe large scale modules often occur depending upon the changes of systemdesigns. However, in the conventional large scale modules assemblingplurality of semiconductor power modules, it is not easy to change themaximum current handling capability or the maximum operating voltage.This results in a problem that the rated specifications of the largescale modules can not be changed rapidly and simply.

[0012] Thus, a large scale module was desired and required which couldeasily change the rated specifications, having structure that could bechanged rapidly corresponding to the various specifications requested byusers with low cost.

SUMMARY OF THE INVENTION

[0013] The present invention is proposed to solve the above mentionedproblems.

[0014] That is, it is therefore an object of the present invention toprovide a semiconductor power module strong in moisture resistance andto provide a large scale module, or an assembly of the semiconductorpower modules.

[0015] Another object of the present invention is to provide asemiconductor power module having a large explosion-proof durability andto provide a large scale module comprising the semiconductor powermodules.

[0016] Still another object of the present invention is to provide asemiconductor power module having a high TFT reliability and a high TCTreliability, and to provide a large scale module comprising thesemiconductor power modules.

[0017] Still another object of the present invention is to provide asemiconductor power module having an excellent power cycle durabilityand to provide a large scale module comprising the semiconductor powermodules.

[0018] Still another object of the present invention is to provide alarge scale module which can adjust the number of semiconductor chipsmounted in a package, or in the large scale module so as to change thepower handling capability and the maximum operating voltage of the largescale module rapidly and easily, and further to provide the large scalemodule having a flexibility of rated performances so that it cancorrespond quickly to various specifications requested by users withoutwasting cost.

[0019] In order to attain the above mentioned objects, the first featureof the present invention lies in a semiconductor power module providedwith: a ceramic substrate; a metallic plate bonded to a surface of thissubstrate; a cylindrical metallic flange which is hermetically bonded toa surface of the substrate at an outer circumference of the substrate,separated from the metallic plate; a disk-shaped ceramic housing forhermetically sealing an opening of this metallic flange; and at leastone or more semiconductor chips mounted on and soldered to the metallicplate on the surface of the ceramic substrate. Here, as thesemiconductor chip, it is possible to use a semiconductor chip mergingvarious semiconductor switching devices, such as an IGBT, a powerMOSFET, a power bipolar transistor (power BJT), a GTO thyristor, a powerstatic induction transistor (power SIT), a static induction thyristor(SI thyristor) and the like. In addition, as the ceramic substrate, itis possible to use various substrates, such as alumina (Al₂O₃), aluminumnitride (AlN), silicon nitride film (Si₃N₄), beryllia (BeO) and thelike.

[0020] According to the first feature of the present invention, ahermetically sealed container is created by the ceramic substrate, thecylindrical metallic flange and the disk-shaped housing. For example,one or more semiconductor chips, such as IGBTs and the like, areaccommodated in this hermetically sealed container. And thishermetically sealed container has a very high air-tightness. Forexample, the air leak rate of less than 10⁻⁴ Pa·m³/sec (10⁻⁵atm·cm³/sec) is easily obtained by this hermetically sealed container.Further, it is practically easy for this hermetically sealed containerto have the higher air-tightness (the lower air leak rate) of, forexample, about 10⁻⁸ Pa·m³/sec (10⁻⁹ atm·cm³/sec) to 10⁻¹⁰ Pa·m³/sec(10⁻¹¹ atm·cm³/sec). In addition, the ceramic substrate, the metallicplate made of, for example, copper, bonded to the surface thereof andthe metallic flange are brazed with silver brazing, aluminum brazing orthe like. Moreover, the brazed portion can be sufficiently strongagainst the thermal stress resulting from the difference of the thermalexpansion coefficient between the ceramic substrate and the metallicplate, or between the ceramic substrate and the metallic flange.

[0021] The second feature of the present invention lies in asemiconductor power module provided with: a ceramic substrate; ametallic plate bonded to a surface of the ceramic substrate; a metallicflange which is hermetically bonded to a surface of the metallic plateat boundary of, or at an outer circumference of the metallic plate; adisk-shaped ceramic housing for hermetically sealing an opening of thismetallic flange; and at least one or more semiconductor chips solderedto the metallic plate on the surface of the ceramic substrate. Here, asthe semiconductor chip, it is possible to use the semiconductor chipmerging the various semiconductor switching devices, such the IGBT, thepower MOSFET, the power BJT, the GTO thyristor, the power SIT, the SIthyristor and the like, similarly to the first feature. In addition, asthe ceramic substrate, it is also possible to use the substrate, such asthe Al₂O₃, the AlN, the Si₃N₄, the BeO or the like, similarly to thefirst feature.

[0022] According to the second feature of the present invention, thecylindrical metallic flange is bonded to the metallic plate made of, forexample, copper or the like, where the metallic plate is bonded on asurface of the ceramic substrate. Thus, if the metallic flange is madeof metal with a low thermal expansion coefficient, the three layeredstructure in which the high thermal expansion coefficient material (themetallic plate) is sandwiched by upper low thermal expansion coefficientmaterial (the metallic flange) and lower low thermal expansioncoefficient material (the ceramic substrate) is constructed. Then, inthe three layered structure, the thermal stress ascribable to thedifference of the thermal expansion coefficient between the ceramicsubstrate and the metallic plate is reduced by the compensating stressacting between the metallic plate and the cylindrical metallic flange.Hence, it is possible to further improve the TFT reliability and the TCTreliability.

[0023] The third feature of the present invention pertains to a largescale module comprising plurality of semiconductor power modules. Here,as the semiconductor power module, it is possible to use thesemiconductor power module described in the above mentioned first andsecond features of the present invention. Namely, the large scale moduleof the third feature comprises: a heat sink; a metallic frame having aplurality of openings disposed on the heat sink; a plurality ofsemiconductor power modules disposed on the heat sink so as to bemounted in the openings; a plurality of sealing members disposed betweenthe respective semiconductor power modules and the metallic frame; aplastic cover for covering one surface of the metallic frame on whichthe semiconductor power module is mounted; and a resin filled into thecover.

[0024] According to the third feature of the present invention, if adesirable number of openings are formed on the metallic frame, it ispossible to mount a desirable number of semiconductor power modules inthe metallic frame. For example , the parallel connection of a desirablenumber of semiconductor power modules enables the formation of the largescale module having a desirable maximum current handling capability andpower handling capability at the maximum operating voltage. In addition,if a desirable number of semiconductor power modules are mounted in themetallic frame and further they are connected in series, it is possibleto assemble the large scale module having desirable operating voltages,desirable breakdown voltages, or desirable blocking voltages. Moreover,the selection and the combination of the parallel connection and theseries connection enables the formation of a large scale module havingany power handling capability and the maximum operating voltages.Therefore, by adjusting the number of semiconductor chips mounted in themetallic frame and selecting/combing the parallel/series connection, itis easy to response to the various specifications of users rapidlywithout costing extra money.

[0025] Further it is easy to construct various inverters or variousconverters having desirable maximum current handling capabilities, thedesirable power handling capabilities, or the desirable maximumoperating voltages, rapidly responding to various specifications imposedby miscellaneous users.

[0026] Other and further objects and features of the present inventionwill become obvious upon an understanding of the illustrativeembodiments about to be described in connection with the accompanyingdrawings or will be indicated in the appended claims, and variousadvantages not referred to herein will occur to one skilled in the artupon employing of the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a cross sectional view showing a configuration of aconventional semiconductor power module;

[0028]FIG. 2A is a plan view showing a structure of a semiconductorpower module according to a first embodiment of the present invention;

[0029]FIG. 2B is a cross sectional view taken on the direction I-I ofFIG. 2A;

[0030]FIG. 2C is a cross sectional view taken on the direction II-IIFIG. 2A;

[0031]FIG. 2D is a cross sectional view taken on the direction III-IIIof FIG. 2A;

[0032]FIG. 2E is a schematic view showing the gate wirings of thesemiconductor power module according to the first embodiment of thepresent invention;

[0033]FIG. 2F is a bird's eye view showing an example of the emitterelectrode member of the semiconductor power module according to thefirst embodiment of the present invention;

[0034]FIG. 3A is a cross sectional view showing a structure of asemiconductor power module according to a second embodiment of thepresent invention, in a plane corresponding to the plane along thedirection I-I of FIG. 2A;

[0035]FIG. 3B is a cross sectional view showing a structure of thesemiconductor power module according to the second embodiment of thepresent invention, in a plane corresponding to the plane along thedirection II-II FIG. 2A;

[0036]FIG. 4 is a cross sectional view showing a structure of a largescale module according to a third embodiment of the present invention;

[0037]FIG. 5 is a cross sectional plan view of the large scale moduleshown in FIG. 4;

[0038]FIG. 6A is a cross sectional view showing a structure of asemiconductor power module according to another embodiment of thepresent invention, in the plane corresponding to the plane along thedirection I-I of FIG. 2A;

[0039]FIG. 6B is a cross sectional view showing a structure of asemiconductor power module according to another embodiment of thepresent invention, in the plane corresponding to the plane along thedirection II-II of FIG. 2A; and

[0040]FIG. 7 is a bird's eye view showing another example of the emitterelectrode member of the semiconductor power module of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Various embodiments of the present invention will be describedwith reference to the accompanying drawings. It is to be noted that thesame or similar reference numerals are applied to the same or similarparts and elements throughout the drawings, and the description of thesame or similar parts and elements will be omitted or simplified.

[0042] Generally and as it is conventional in the representation ofsemiconductor devices, it will be appreciated that the various drawingsare not drawn to scale from one figure to another nor inside a givenfigure, and in particular that the layer thickness are arbitrarily drawnfor facilitating the reading of the drawings.

[0043] First Embodiment

[0044]FIG. 2A is a cross sectional plan view showing the structure of asemiconductor power module according to a first embodiment of thepresent invention. FIGS. 2B, 2C and 2D are cross sectional views takenon the direction I-I, the direction II-II and the direction III-III ofFIG. 2A, respectively. As shown in FIG. 2A, the semiconductor powermodule according to the first embodiment of the present inventioncomprises four semiconductor chips 351, 352, 353 and 354 merging IGBTsrespectively on their chips, the four semiconductor chips 351, 352, 353and 354 are mounted on a ceramic substrate 31, and the periphery thereofis surrounded with a circular flange 32 made of metal with low thermalexpansion coefficient. On the semiconductor chips 351, 352, 353 and 354,emitter electrode pads 381, 382, 383 and 384 and gate electrode pad 391,392, 393 and 394, each made of metallic thin film such as aluminum thinfilm or aluminum alloy (Al—Si, Al—Cu—Si) thin film, are disposedrespectively.

[0045] As shown in FIGS. 2B, 2C and 2D , a copper plate 331 is bonded tothe top surface of the ceramic substrate 31, and a copper plate 332 isbonded to the bottom surface thereof, by the brazing, such as the silverbrazing, the aluminum brazing or the like, respectively. The flange 32is bonded to the outer side of the copper plate 331 at the boundary ofand on the top surface of the ceramic substrate 31, similarly by thebrazing, such as the silver brazing, the aluminum brazing or the like.Such brazing is conducted based on “an activated metallizing method”using surface catalyst, such as titanium (Ti) and the like. Such brazingenables the bonding interfaces between the ceramic substrate 31 and thecopper plate 331, 332 and between the ceramic substrate 31 and theflange 32 to be bonded under excellently mechanical strength. As amatter of fact, brazing layers each having a thickness of 2 to severalmicrons are present on the respective bonding interfaces between theceramic substrate 31 and the copper plates 331, 332 and between theceramic substrate 31 and the flange 32. However, the explanationsthereof on FIGS. 2B, 2C and 2D are omitted to avoid cluttering up thedrawing.

[0046] A semiconductor chip 351 is soldered onto the copper plate 331through a solder 341 having a thickness of about 100 μm, and asemiconductor chip 352 is also soldered onto the copper plate 331through a solder 342. An emitter pedal (conductive electrode pedal) 361of emitter electrode member made of molybdenum (Mo) is pushed against anIGBT emitter electrode pad disposed on a main surface of thesemiconductor chip 351 by a spring 37 through a plurality of metallichemispheres or bumps 366, such as solder balls, silver bumps and thelike. Similarly, an emitter pedal (conductive electrode pedal) 362 ofemitter electrode member is pushed against an emitter electrode paddisposed on a main surface of the semiconductor chip 352 by the spring37 through a plurality of metallic hemispheres 366. The othersemiconductor chips 353, 354, although they are arranged at the back ofthe page and are not shown, have the structures similar to those of thesemiconductor chips 351, 352. The emitter pedals (conductive electrodepedals) 361, 362 for contacting with the respective emitter electrodesvia the metallic hemispheres 366 are connected to backbone 36 of theemitter electrode members, as shown in FIG. 2F. On the bottom surface ofeach emitter pedals (conductive electrode pedals) 361 to 364, theplurality of metallic hemispheres 366 are attached. In this way, thefour emitter pedals (conductive electrode pedals) 361 to 364 of theemitter electrode members are pressure-contacted to the respectiveemitter electrode pads with low Ohmic contact resistance to accordinglyform emitter electrode paths. As shown in FIG. 2B, the spring 37generates the pushing force against the four emitter pedals 361 to 364since it is pushed from above by a ceramic housing 38.

[0047] Although, on every bottoms surface of emitter pedals (conductiveelectrode pedals) 361 to 364, the plurality of metallic hemispheres 366are attached to be pressure-contacted with the emitter electrode pads inFIG. 2F, it is possible to employ the emitter pedals having flat bottomsurfaces. In this case, we should prepare copper (Cu) foils, each havingthe plurality of metallic hemispheres. Then the copper foils arerespectively sandwiched between the emitter pedals having the flatbottom surfaces and emitter electrode pads, and the copper foils arepressure-contacted to the respective emitter electrode pads by employingthe similar spring force applied on the top surface of the emitterpedals.

[0048] An annular member 39 made of metal with low thermal expansioncoefficient is connected to a boundary end of the ceramic housing 38with the brazing, such as the silver brazing and the like. Then, theupper portion of this annular member 39 is welded to the top end of theflange 32.

[0049] In addition, as shown in FIG. 2D, gate probe pins 471 and 472 arepushed against the IGBT gate electrode pads 391 and 392 (see FIG. 2A)disposed on the respective main surfaces of the four semiconductor chips351 to 354 via insulators 481 and 482 through springs not shown in thefigure. Similarly, at the back of the FIG. 2D, gate probe pins 473 and474 (not shown) are pushed against the IGBT gate electrode pads 393 and394 (see FIG. 2A). As shown in FIG. 2E, four gate probe pins 471 to 474converge on a single gate conductive pillar 45 made of copper throughsheathed cables (or coaxial cables) 451-454 and 456-459. At the midpoints of respective sheathed cables, four gate resisters 461-464 havingthe required resistance are intervened.

[0050] Bottom surfaces serving as collectors of the four semiconductorchips 351 to 354 are soldered to the copper plate 331, respectively.Thus, the copper plate 331 serves as an IGBT collector electrode wiringportion. A collector conductive pillar 40 made of copper is verticallyerected near the center of this copper plate 331 by the soldering. Then,as shown in FIG. 2C, it penetrates the backbone 36 of the emitterelectrode member, and further penetrates the ceramic housing 38, andprojects towards external portion.

[0051] In addition, an emitter conductive pillar 41 made of copper isuprightly erected on the backbone 36 of the emitter electrode member,and it penetrates the ceramic housing 38 and then projects towards theexternal portion. The collector conductive pillar 40 is tightlyconnected to a cap-shaped external collector electrode 42 made of copperthat is uprightly bonded on the ceramic housing 38 by the brazing, suchas the silver brazing, the aluminum brazing or the like, with calking.Similarly, the emitter conductive pillar 41 is tightly connected to acap-shaped external emitter electrode 43 made of copper uprightly bondedon the ceramic housing 38 by the brazing, with the calking. Further, thegate conductive pillar 45 is tightly connected to a cap-shaped externalgate electrode 44 made of copper uprightly bonded on the ceramic housing38 by the brazing, with the calking.

[0052] According to the first embodiment of the present invention, thelower end of the flange 32 is brazed to the ceramic substrate 31, andthe upper end thereof is brazed to the ceramic housing 38 through themember 39 made of the metal with the low thermal expansion coefficientthat is welded and connected to the flange 32, and thereby thehermetically sealed space is created. Moreover, the penetration holes ofthe collector conductive pillar 40, the emitter conductive pillar 41 andgate conductive pillar 45 which project above the ceramic housing 38 areair-tightly blocked with the cap-shaped external collector electrode 42,the cap-shaped external emitter electrode 43 and the cap-shaped externalgate electrode 44 by the brazing. Thus, a container has an extremelyhigh air-tightness of about 10⁻⁸ Pa·m³/sec(10⁻⁹ atm·cm³/sec) to 10⁻¹⁰Pa·m³/sec (10⁻¹¹ atm·cm³/sec). Accordingly, this can make the moistureresistance very higher, and perfectly prevent humidity, corrosive gasand the like from invading the container and also prevent the trouble ofthe four semiconductor chips 351 to 354. Hence, this can extremelyimprove the reliability.

[0053] A metallic material whose thermal expansion coefficient is closeto that of the ceramic, such as 42 Alloy, 36 Alloy or the like, isdesirable for the material of the flange 32. In addition, these metalsare strong in mechanical strength and also strong in brazing stress.Thus, an annealed material is desirable in order to drop the mechanicalstrength. It is possible to select such a material to largely reduce thethermal stress resulting from the difference of the thermal expansioncoefficient between the respective members to further improve the TFTreliability and the TCT reliability.

[0054] In addition, the metal and the ceramic are bonded to each otherby the welding and the brazing to accordingly form the hermeticallysealed container. Thus, the mechanical strength thereof is extremelylarger than that of the plastic or the like. Hence, even if thesemiconductor chips 351, 352, . . . are exploded by the short circuitfailure and the like, the hermetically sealed container is never brokendue to the sufficient explosion-proof durability, which improves thesafety.

[0055] Moreover, each emitter electrode pad of the semiconductor chips351, 352, . . . is connected to the external emitter electrode 43projecting above the ceramic housing 38 by pressure-contacting theemitter electrode member 36 through the metallic hemispheres 366 withoutusing a bonding wire such as an aluminum wire and the like. Further,each collector electrode layer on the bottom surfaces of thesemiconductor chips 351, 352, . . . is bonded to the external collectorelectrode 42 on the ceramic housing 38 by the soldering to the copperplate 331. Thus, the conductive capacity on each electrode path canmanifest an extremely large value. The electrode paths constituting thesemiconductor power module are created by such conductive members havingthe large conductive capacity, which can extremely improve the powercycle durability of the semiconductor power module. For example, it ispossible to easily achieve the power cycle durability of about tenmillion times or more at the junction temperature variation ΔT_(j)=40°C. and the case temperature of T_(c)=50° C., and also possible toachieve the power cycle durability of about one hundred thousand timesor more at the junction temperature variation ΔT_(j)=100° C. and thecase temperature of T_(c)=50° C.

[0056] In addition, since the semiconductor power module according to afirst embodiment of the present invention does not require the metalliccooling plate 1, which has been inevitable to the conventionalsemiconductor power module, even if the thermal expansion coefficientsof the ceramic substrate 31 and the copper plate 331 are different fromeach other, the crack is not induced. Hence, it is possible to improvethe TCT durability. For example, it is possible to easily achieve theTCT reliability of about 1000 cycles or more at T_(c)=165° C.

[0057] In addition, since the dimension of the semiconductor powermodule according to the first embodiment can be made substantiallyidentical to those of the conventional modules, the similar dimensionspecification can be used.

[0058] As detailed above, in the semiconductor power module according tothe first embodiment of the present invention, the plurality ofsemiconductor chips are accommodated in the container that ishermetically sealed by the metal and the ceramic to have the highair-tightness. Then, the emitter electrode pads disposed on the topsurface of the semiconductor chips are respectively connected to theconductive member having the large conductive capacity by thepressure-contacting. Moreover, the brazing, such as the silver brazing,the aluminum brazing or the like is performed on the portion receivingthe thermal stress. Then, the metallic cooling plate is removed. Thus,this can improve the moisture resistance, the explosion-proofdurability, the TFT reliability and the TCT reliability and the powercycle durability to thereby make the property of the semiconductor powermodule extremely higher.

[0059] Second Embodiment

[0060]FIGS. 3A and 3B are cross sectional views showing a structure of asemiconductor power module according to a second embodiment of thepresent invention. Also, four semiconductor chips are mounted on theceramic substrate 31, in the semiconductor power module according to thesecond embodiment of the present invention. A plan view thereof isomitted since it is identical to that of the first embodiment of thepresent invention. That is, FIG. 3A is a cross sectional view in a planecorresponding to a plane along the direction I-I of FIG. 2A, shown asthe plan view of the first embodiment of the present invention, and FIG.3B is a cross sectional view in a plane corresponding to a plane alongthe direction II-II FIG. 2A. Respective IGBTs are merged on the foursemiconductor chips.

[0061] As shown in FIGS. 3A and 3B, in the semiconductor power moduleaccording to the second embodiment of the present invention, a copperplate 331 is bonded to a top surface of a ceramic substrate 31 with thebrazing, such as the silver brazing, the aluminum brazing or the like.This copper plate 331 is a circular plate having a larger diameter thanthat of the copper plate of the first embodiment of the presentinvention. Moreover, a cylindrical flange 32 made of metal with lowthermal expansion coefficient is bonded onto this copper plate 331 withthe brazing, such as the silver brazing, the aluminum brazing or thelike. The bottom surface of a semiconductor chip 351 is soldered to thiscopper plate 331 through a solder 341, and the bottom surface of asemiconductor chip 352 is soldered thereto through a solder 342. Sincethe bottom surfaces of the semiconductor chips 351, 352 are IGBTcollector electrode layers, the copper plate 331 serves as an IGBTcollector electrode wiring portion. In addition, the flange 32 made ofthe metal with the low thermal expansion coefficient is electricallybonded to the copper plate 331. Thus, the flange 32 also doubles as thecollector electrode of the semiconductor power module.

[0062] As shown in FIG. 3B, a cap-shaped external emitter electrode 43and a cap-shaped external gate electrode 44 are uprightly bonded on aceramic housing 38 with the brazing in the semiconductor power moduleaccording to the second embodiment of the present invention. Then, thiscap-shaped external emitter electrode 43 is tightly connected an emitterelectrode pillar 41 uprightly erected on a backbone 36 of emitterelectrode member with the calking. The cap-shaped external gateelectrode 44 is tightly connected an gate electrode pillar 45 to whichfour gate probe pins converge. The other structure is similar to that ofthe first embodiment shown in FIGS. 2A, 2B and 2C.

[0063] In the semiconductor power module according to the secondembodiment of the present invention, the flange 32 made of the metalwith the low thermal expansion coefficient is bonded onto the copperplate 331 with the brazing. That is, the ceramic substrate 31 having asmall thermal expansion coefficient is fixed on the bottom surface ofthe copper plate 331 having a large thermal expansion coefficient, andthe flange 32 having a small thermal expansion coefficient is fixed onthe top surface of the copper plate 331. Thus, the thermal expansion ofthe copper plate 331 is suppressed from both the sides. In this way, thesuppression of the thermal expansion of the copper plate 331 enables theTCT durability of the second embodiment to be improved over that of thefirst embodiment.

[0064] In addition, it is not necessary to provide a dedicated externalcollector electrode on the ceramic housing 38 since the flange 32doubles as the external collector electrode without reducing the powercycle durability. Correspondingly, this can make the apparatus smallerto simultaneously simplify a process of assembling the semiconductorpower module to thereby improve the productivity. The other structure issimilar to that of the first embodiment shown in FIGS. 2A and 2B.Moreover this structure provides the similar effectiveness andadvantages as those of the first embodiment.

[0065] As detailed above, in the semiconductor power module according tothe second embodiment of the present invention, the semiconductor chipsare accommodated in the container that is created by the metal and theceramic and has the high air-tightness. Then, the emitter pedals 361,362, . . . are contacted to emitter electrode pads of the semiconductorchips 351, 352, . . . through the metallic hemispheres 366 without usinga bonding wire such as an aluminum wire and the like so that theconductive capacity on the electrode path to the external emitterelectrode 43 can manifest an extremely large value. Moreover, thebrazing is performed on the portion receiving the thermal stress.Furthermore, the metallic cooling plate can be removed. Thus, this canimprove the moisture resistance, the explosion-proof durability, the TFTreliability and the TCT reliability and the power cycle durability tothereby make the performance of the semiconductor power module extremelyhigher.

[0066] Third Embodiment

[0067]FIG. 4 is a vertical cross sectional view taken on the directionIII-III of FIG. 5, which is a cross sectional plan view of the largescale module according to the third embodiment of the present invention.

[0068] As shown in FIG. 5, a flange (metallic frame) 51 constituting theouter contour of the large scale module according to the thirdembodiment of the present invention has a rectangular plane and has aplurality of (six) screw stop holes 61 to 66 in the periphery thereof.Then, this flange (metallic frame) 51 has a plurality of (four) circularopenings 52 for accommodating a plurality of (four) semiconductor powermodules 81 to 84. Although the opening 52 is circular in FIG. 5, it isnaturally allowable that the opening 52 is rectangular, hexagonal orother shapes.

[0069] As shown in FIG. 4, a plastic cover 54 is adhered and bonded tothe upper portion of the screw stop flange 51 through a resin basedadhesive 74 and the like. This plastic cover 54 covers semiconductorpower modules 81 to 84. That is, six screws (not shown) penetrate thesix screw stop holes 61 to 66 shown in FIG. 5, respectively. Then, theflange (metallic frame) is fixed on a large heat sink 60 with thescrews. Accordingly, the plastic cover 54 pushes down the semiconductorpower modules 81 to 84 at a constant pressure. As a result, thesemiconductor power modules 81 to 84 are pushed against the heat sink 60and fixed therein. For example, as these four small semiconductor powermodules 81 to 84, the semiconductor power module shown in FIGS. 3A and3B in accordance with the second embodiment of the present invention canbe employable. As shown in FIG. 4, sealing members or sealing rubbers(sealing rings) 53 are mounted in and under the protruding tongues ofthe openings 52, the sealing members (the sealing rubbers) 53 arepositioned between the outer edges of the semiconductor power modules 81to 84 and the protruding tongues of the flange 51, respectively. Thus,the inside of the plastic cover 54 is hermetically sealed by the factthat the protruding tongues of the flange 51 pushes down the outer edgesof the semiconductor power modules 81 to 84 through the sealing members(the sealing rubbers) 53.

[0070] An outer emitter electrode 57, an outer collector electrode 38and an outer gate electrode (not shown in FIG. 4) are positioned overthe plastic cover 54 as electrodes of the large scale module accordingto the third embodiment of the present invention. The semiconductorpower modules 81, 82 . . . .may comprise the ceramic substrate 31, aplurality of semiconductor chips having the IGBTs mounted on the ceramicsubstrate 31 and the flange 32 surrounding the periphery of thesemiconductor chips, similarly to the first or second embodiments. TheIGBT emitter electrodes 36 disposed on the ceramic housings 38 over thesemiconductor power modules 81, 82, . . . are connected in parallel toeach other through conductive materials 55. And the IGBT collectorelectrodes 32 doubling as the flange 32 are connected in parallel toeach other through another conductive materials 56. Although not shownin the figure, the IGBT gate electrodes disposed on the ceramic housingsover the semiconductor power modules 81, 82, . . . are connected inparallel to each other through another conductive materials. Theseconductive materials 55, 56 are bonded to the upper portion of theplastic cover 54 and connected to the outer emitter electrode 57 and theouter collector electrode 58. Moreover, the inside of the plastic cover54 is filled with a gelled silicon resin 59, epoxy resin or the like, inorder to make the mechanical strength and the insulation strengthhigher.

[0071] According to the third embodiment of the present invention, thelarge scale module is assembled by mounting the plurality ofsemiconductor power modules 81 to 84 (four, in the third embodiment ofthe present invention) into the screw stop flanges 51 and thenconnecting them parallel to each other. Thus, it is possible to easilyachieve a desirable maximum current handling capability by freelyselecting the number of semiconductor power modules 81, 82, . . . to beused. Hence, the large scale module according to the third embodiment ofthe present invention can response to various power and voltagespecifications requested by users and design changes thereof rapidly andeasily.

[0072] In addition, the third embodiment of the present invention showsthe example in which the semiconductor power modules 81, 82, . . . areelectrically connected parallel to each other. However, they may beconnected in series. It is possible to connect the predetermined numberof semiconductor power modules 81, 82, . . . in series to easily achievea predetermined breakdown voltage and a blocking voltage requested bythe users and also response to various circuit specifications requestedby the users and miscellaneous design changes thereof rapidly andeasily.

[0073] For example, the suburban train requires the large scale modulehaving the rated specification of the 800A, 3300V class or the 1200A,3300V class. The long-distance high speed trains require the largeroperating namely “the Shinkansen” super express train in Japan demandsthe large scale module having the rated specification of the 1200A,4500V class. On the other hand, “the ICE” train in Germany/Switzerlandand “the TGV” train in France require higher voltage type large scalemodule having the rated specification of the 1200A, 6500V class. In thelarge scale module according to the third embodiment of the presentinvention, it is possible to adjust the number of semiconductor powermodules to be mounted in the metallic frame and to select the bestcombination of the series connection and the parallel connection tothereby change the maximum power handling capability and the maximumoperating voltage of the large scale module, without wasting furthertime and efforts. And further, it is easy to response rapidly to thevarious specifications requested by different users and the designchanges, without requiring further increase of manufacturing cost.

[0074] Other Embodiments

[0075] Various modifications will become possible for those skilled inthe art after receiving the teachings of the present disclosure withoutdeparting from scope thereof.

[0076] For example, it is also possible to combine the structure of thesemiconductor power module according to the first and the secondembodiments of the present invention to thereby put both the merits tothe practical use. FIGS. 6A and 6B are cross sectional views showing astructure of a semiconductor power module in which the first and thesecond embodiments of the present invention are combined. FIG. 6A is across sectional view in the plane corresponding to the plane along thedirection I-I of FIG. 2A, shown as the plan view of the first embodimentof the present invention. FIG. 6B is a cross sectional view in the planecorresponding to the plane along the direction II-II of FIG. 2A. FourIGBTs are merged in respective four semiconductor chips.

[0077] As shown in FIGS. 6A and 6B, a copper plate 331 having a largediameter similar to that of the second embodiment is bonded to thesemiconductor power module according to another embodiment of thepresent invention. Moreover, a flange 32 is bonded onto this copperplate 331 with the brazing. Bottom surfaces of semiconductor chips 351,352 are soldered to this copper plate 331 through solders 341, 342,respectively. The copper plate 331 serves as a collector electrodewiring portion of IGBT. In addition, the flange 32 made of metal withlow thermal expansion coefficient is electrically bonded to the copperplate 331. However, differently from the second embodiment, the flange32 does not function as the collector electrode of the semiconductorpower module. Separately, a dedicated cap-shaped external collectorelectrode 42 made of copper is prepared and uprightly onded on a ceramichousing 38 with the brazing, as shown in FIGS. 6A and 6B. This structureof the external collector electrode 42 is similar to that of the firstembodiment of the present invention. That is, a collector conductivepillar 40 made of copper is uprightly erected near the center of thecopper plate 331. Then, this collector conductive pillar 40 penetrates abackbone 36 of an emitter electrode member, and further penetrates theceramic housing 38 and projects towards external portion. This collectorconductive pillar 40 is connected to the external collector electrode 42with the calking. The structure of an external emitter electrode 43 andan external gate electrode 44 are similar to those of the first andsecond embodiments. Thus, the explanation thereof is omitted.

[0078] According to the semiconductor power module shown in FIGS. 6A and6B, the thermal expansion of the copper plate 331 is suppressed by themembers which are bonded on both the surfaces and have small thermalexpansion coefficients. In this way, the suppression of the thermalexpansion of the copper plate 331 can improve the TCT durability. Inreview, the flange 32 has served as the collector electrode in thesecond embodiment of the present invention. However, in a case of theflange 32 made of the metal with the low thermal expansion coefficient,it is difficult to make an electric resistance thereof smaller. So, thisinvolves the increase of the forward voltage drop and the heatdissipation in the flange 32, and also makes the electromagnetic shieldinsufficient. On the contrary, the dedicated collector conductive pillar40 and cap-shaped external collector electrode 42 made of the materialwith the small electric resistance are provided in the semiconductorpower module as shown in FIGS. 6A and 6B so as to improves thedisadvantages in the second embodiment. Thus, it is possible to improvethe TCT durability while ensuring the small resistances of the externalcollector electrode and the collector electrode fetching portionconnected to this external collector electrode. Moreover, the moistureresistance, the explosion-proof durability and the power cycledurability can be improved similarly to the first and secondembodiments.

[0079] The structure of the emitter electrode members is not limited asshown in FIG. 2F. FIG. 7 is a bird's eye view showing another example ofthe emitter electrode member of the semiconductor power module of thepresent invention. In FIG. 7, four emitter pedals (conductive electrodepedals) 361 to 364 and backbone 36 of emitter electrode member are madeof relatively thin plate of metal—such as molybdenum (Mo)—as a singlebody by punching and mechanical press. Further, each emitter pedals(conductive electrode pedals) 361 to 364 is pressed to form a pluralityof metallic hemispheres 366 protruding downward from the bottom surfaceof each emitter pedals 361 to 364. Then the emitter pedals 361 to 364can contact with the emitter electrode pads disposed on thesemiconductor chip via the metallic hemispheres 366 with the aid of thespring, pushing force against the top surface of emitter pedals 361 to364. And an emitter conductive pillar 41 is brazed on top surface ofbackbone 36 to erect upwards.

[0080] Of course, the semiconductor power module and the large scalemodule in the present invention are not limited to the semiconductorpower module or the large scale module used in the power converter forthe system of driving the railcar. They can be applied to a groundfacility for supplying electric power to the electric railcars or asystem of driving linear motor cars, and can be also applied to a caseof rotating a screw by using an electric motor with a power generated byan internal combustion engine installed in a ship. Moreover, thesemiconductor power module and the large scale module in the presentinvention can be applied to various motor drive applications such as inan electric vehicle, an elevator, an escalator or the like. In addition,they can be applied to various inverters/converters in miscellaneousfields, such as an electric power field, an energy field, acommunication field and the like.

[0081] As mentioned above, the present invention naturally includesvarious embodiments which are not described here. Therefore, thetechnical range of the present invention is defined only by thefollowing claims.

What is claimed is:
 1. A semiconductor power module comprising: (a) aceramic substrate; (b) a metallic plate bonded to a surface of saidsubstrate; (c) a cylindrical metallic flange which is hermeticallybonded to said substrate at an outer circumference of said substrate,separated from said metallic plate; (d) a disk-shaped ceramic housingfor hermetically sealing an opening of said metallic flange; and (e) atleast one or more semiconductor chips mounted on and soldered to saidmetallic plate.
 2. The semiconductor power module of claim 1, wherein anannular metallic member is bonded to an outer circumference of saidceramic housing, and an end of said metallic member is bonded to an openend of said metallic flange with a welding.
 3. The semiconductor powermodule of claim 1, wherein bottom surface of said semiconductor chip andsaid metallic flange are electrically connected to each other throughsaid metallic plate.
 4. The semiconductor power module of claim 1,wherein an electrode path is formed by pressure-contacting a conductiveelectrode pedal to an electrode pad disposed on said semiconductor chip.5. The semiconductor power module of claim 4, wherein in said ceramichousing, said conductive electrode pedal is pressure-contacted to saidsemiconductor chip through a pressure applied by a spring.
 6. Thesemiconductor power module of claim 1, wherein said metallic flange is ametal having a small thermal expansion coefficient.
 7. The semiconductorpower module of claim 1, wherein said semiconductor chip is IGBT.
 8. Asemiconductor power module comprising: (a) a ceramic substrate; (b) ametallic plate bonded to a surface of said substrate; (c) a cylindricalmetallic flange which is hermetically bonded to a surface of saidmetallic plate at a boundary of said metallic plate; (d) a disk-shapedceramic housing for hermetically sealing an opening of said metallicflange; and (e) at least one or more semiconductor chips mounted on andsoldered to said metallic plate.
 9. The semiconductor power module ofclaim 8, wherein an annular metallic member is bonded to an outercircumference of said ceramic housing, and an end of said metallicmember is bonded to an open end of said metallic flange with a welding.10. The semiconductor power module of claim 8, wherein bottom surface ofsaid semiconductor chip and said metallic flange are electricallyconnected to each other through said metallic plate.
 11. Thesemiconductor power module of claim 8, wherein an electrode path isformed by pressure-contacting a conductive electrode pedal to anelectrode pad disposed on said semiconductor chip.
 12. The semiconductorpower module of claim 11, wherein in said ceramic housing, saidconductive electrode pedal is pressure-contacted to said semiconductorchip through a pressure applied by a spring.
 13. The semiconductor powermodule of claim 8, wherein said metallic flange is a metal having asmall thermal expansion coefficient.
 14. The semiconductor power moduleof claim 8, wherein said semiconductor chip is IGBT.
 15. A large scalemodule comprising: (a) a heat sink; (b) a metallic frame having aplurality of openings disposed on said heat sink; (c) a plurality ofsemiconductor power modules disposed on said heat sink so as to bemounted in said openings; (d) a plurality of sealing members disposedbetween said respective semiconductor power modules and said metallicframe; (e) a plastic cover for covering one surface of said metallicframe on which said semiconductor power module is mounted; and (f) aresin filled into said cover.
 16. The large scale module of claim 15,wherein respective electrodes of said semiconductor power module areconnected in parallel or in series and connected to outer electrodesdisposed on a top surface of said cover.
 17. The large scale module ofclaim 15, wherein a second surface opposite to a first surface attachedto the heat sink is covered by said plastic cover.
 18. The large scalemodule of claim 15, wherein said semiconductor power module comprising:(a) a ceramic substrate; (b) a metallic plate bonded to a surface ofsaid substrate; (c) a cylindrical metallic flange which is hermeticallybonded to said substrate at an outer circumference of said substrate,separated from said metallic plate; (d) a disk-shaped ceramic housingfor hermetically sealing an opening of said metallic flange; and (e) atleast one or more semiconductor chips mounted on and soldered to saidmetallic plate.
 19. The large scale module of claim 15, wherein saidsemiconductor power module comprising: (a) a ceramic substrate; (b) ametallic plate bonded to a surface of said substrate; (c) a cylindricalmetallic flange which is hermetically bonded to a surface of saidmetallic plate at a boundary of said metallic plate; (d) a disk-shapedceramic housing for hermetically sealing an opening of said metallicflange; and (e) at least one or more semiconductor chips mounted on andsoldered to said metallic plate.